[wp] Introduces table abstract type for offsets

src/plugins/wp/MemMemory.ml

src/plugins/wp/share/coqwp/Memory.v

src/plugins/wp/share/why3/frama_c_wp/memory.mlw

src/plugins/wp/tests/wp_acsl/oracle/base_offset.res.oracle

...t.1.session/script/init_t2_bis_v2_assigns_exit_part2.json

...1.session/script/init_t2_bis_v2_assigns_normal_part2.json

...t.1.session/script/init_t2_bis_v2_loop_assigns_part2.json

...t.1.session/script/init_t2_bis_v2_loop_assigns_part3.json